CVE-2026-93261: locking/lockdep: Fix NULL pointer dereference in __lock_set_class()

CVE-2026-93261: locking/lockdep: Fix NULL pointer dereference in __lock_set_class()

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

locking/lockdep: Fix NULL pointer dereference in __lock_set_class()

register_lock_class() can return NULL when the lock class pool is
exhausted, graph_lock() fails, or key validation fails. However,
__lock_set_class() uses the return value directly in pointer arithmetic
without a NULL check:

  class = register_lock_class(lock, subclass, 0);
  hlock->class_idx = class - lock_classes;

If class is NULL, this computes a wild offset that corrupts
hlock->class_idx. The subsequent reacquire_held_locks() call will
invoke hlock_class() with this corrupted index, leading to a NULL or
out-of-bounds pointer dereference.

Add the missing NULL check, consistent with how __lock_acquire() already
handles this case at the same call site.

The Linux kernel CVE team has assigned CVE-2026-93261 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 2.6.27 with commit 64aa348edc617dea17bbd01ddee4e47886d5ec8c and fixed in 5.10.270 with commit f6093ff67ea6e347574819ed23e96e0f82a25ffc
	Issue introduced in 2.6.27 with commit 64aa348edc617dea17bbd01ddee4e47886d5ec8c and fixed in 5.15.221 with commit 59a5c7dd331a3dab48100e1ef8e9bb4f9132a2b2
	Issue introduced in 2.6.27 with commit 64aa348edc617dea17bbd01ddee4e47886d5ec8c and fixed in 6.1.188 with commit f56e54fd24f05e9de528fcb77f6084f80c8066ce
	Issue introduced in 2.6.27 with commit 64aa348edc617dea17bbd01ddee4e47886d5ec8c and fixed in 6.6.157 with commit 5c3bff6cf26e6a54fbf8b893a879c32824d2d50d
	Issue introduced in 2.6.27 with commit 64aa348edc617dea17bbd01ddee4e47886d5ec8c and fixed in 6.12.110 with commit b2113dcd8238bf00ce37a34e67b29cf31d32a545
	Issue introduced in 2.6.27 with commit 64aa348edc617dea17bbd01ddee4e47886d5ec8c and fixed in 6.18.52 with commit e7c69c6695d84220847cca62a45e879e71e79e9d
	Issue introduced in 2.6.27 with commit 64aa348edc617dea17bbd01ddee4e47886d5ec8c and fixed in 7.2.6 with commit 9be10f49dfc2e4b472b3a5f346483b67374774b8
	Issue introduced in 2.6.27 with commit 64aa348edc617dea17bbd01ddee4e47886d5ec8c and fixed in 7.3-rc1 with commit 7577e00b9ab506202b9f1a33de3cc8cc6413a4db

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-93261
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	kernel/locking/lockdep.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/f6093ff67ea6e347574819ed23e96e0f82a25ffc
	https://git.kernel.org/stable/c/59a5c7dd331a3dab48100e1ef8e9bb4f9132a2b2
	https://git.kernel.org/stable/c/f56e54fd24f05e9de528fcb77f6084f80c8066ce
	https://git.kernel.org/stable/c/5c3bff6cf26e6a54fbf8b893a879c32824d2d50d
	https://git.kernel.org/stable/c/b2113dcd8238bf00ce37a34e67b29cf31d32a545
	https://git.kernel.org/stable/c/e7c69c6695d84220847cca62a45e879e71e79e9d
	https://git.kernel.org/stable/c/9be10f49dfc2e4b472b3a5f346483b67374774b8
	https://git.kernel.org/stable/c/7577e00b9ab506202b9f1a33de3cc8cc6413a4db